The present invention relates to a process for producing a display device wherein electrophoretic particles or charged migrating particles are moved to effect a display.
In recent years, accompanying the progress of data processing apparatus, there has been an increasing demand for a display device requiring a small power consumption and a small thickness, and extensive study and development have been made on devices satisfying such a demand. Among these, a liquid crystal display device wherein an alignment of liquid crystal molecules is electrically controlled to change optical characteristics has been extensively developed and commercialized as a display device satisfying the demand described above.
As another type of display device, an electrophoretic display device has been proposed by Harold D. Less, et al. (U.S. Pat. No. 3,612,758). FIGS. 8A and 8B illustrate a structure and an operation principle of the electrophoretic display device. Referring to these figures, a display device P3 includes a pair of substrates 1a and 1b disposed with a prescribed gap therebetween and having electrodes 36 and 37, respectively, thereon. The gap between the substrates 1a and 1b is filled with a mixture of positively charged and colored multitude of electrophoretic particles 5 and a dispersion liquid 4 containing a dye so as to be colored in a color different from that of the electrophoretic particles 5. Further, partitioning walls 3 are disposed to divide the gap between the substrates into a plurality of pixels 2 (only one of which is shown in FIGS. 8A and 8B) arranged over an extension of the substrates while preventing the localization of the electrophoretic particles 5 and determine the gap between the substrates 1a and 1b. 
In such a display device P3, when a positive voltage is applied to an upper electrode 36 (as shown) relative to a negative voltage applied to a lower electrode 37, the positively charged electrophoretic particles 5 are moved to be collected so as to cover the lower electrode 37, whereby the pixel exhibits the color of the dispersion liquid 4 when the pixel (display device) is viewed in an indicated arrow A direction (FIG. 8A). On the other hand, when a negative voltage is applied to the upper electrode 36 relative to a positive voltage relative to the lower electrode 37, the positively charged electrophoretic particles 5 are moved and collected to cover the upper electrode 36, whereby the pixel exhibits the color of the electrophoretic particles 5 when the pixel (display device) is viewed in the arrow A direction (FIG. 8B). By effecting such a drive for each of the plurality (or multitude) of pixels, an arbitrary picture is displayed on the display device.
In the above-described display device P3, it is desired that the respective pixels 2 exhibit a substantially uniform color density, and for this purpose, the electrophoretic particles are distributed in substantially equal quantities to the respective pixels. Several processes have been proposed as follows.
Japanese Laid-Open Patent Application (JP-A) 64-86117 has disclosed a process wherein the partitioning walls 3 are formed of a material that is swollen (to increase its volume) by impregnation with the dispersion liquid 4, and the electrophoretic particles 5 are dispersed together with the dispersion liquid 4 over the partitioning walls 3 before the swelling thereof, followed by swelling of the walls 3 to form the pixels 2.
JP-A 2-223935 has disclosed a process wherein one substrate 1a (or 1b) provided with the partitioning walls 3 is dipped within the dispersion liquid 4 containing the electrophoretic particles dispersed therein, and in this state, a flexible film constituting the other substrate 1b (or 1a) is sequentially press-bonded to the substrate 1a (or 1b).
However, even by any of the above processes, there is a certain limit for distribution of the electrophoretic particles 5 in substantially equal amounts to the respective pixels, whereby the respective pixels 2 are caused to exhibit somewhat different color densities, thus resulting in an inferior display quality.
The reason for difficulty of distribution in substantially equal amounts of the electrophoretic particles 5 to the respective pixels is as follows. In the above-described former process, the dispersion liquid 4 is distributed or injected from one side to the other side over an extension of the substrate, but as the charged electrophoretic particles 5 are contained therein, the particles are attached to the surfaces of the substrate and the partitioning walls 3, whereby the particles 5 fail to uniformly reach the corners of the substrate but are liable to form a density distribution which is higher at the upstream side and lower at the downstream side. On the other hand, in the latter process, due to various factors, such as different heights of the walls 3 or a fluctuation in pressing force for sequentially press-bonding the flexible film, the amounts of the dispersion liquid 4 distributed to the respective pixels are liable to be different, thus causing corresponding differences in amounts of the electrophoretic particles 5 distributed to the respective pixels 2.
Accordingly, a principal object of the present invention is to provide a process for producing a display device in which electrophoretic particles as a displaying medium are distributed evenly to respective pixels, thereby obviating a deterioration of display quality.
According to the present invention, there is provided a process for producing a display device of the type comprising: a pair of substrates disposed opposite to each other with a gap therebetween, partitioning walls disposed to divide the gap so as to define a plurality of pixels arranged along an extension of the substrates, an electrophoretic mixture comprising a dispersion liquid and a multitude of charged electrophoretic particles distributed to each pixel, and a first electrode and a second electrode disposed at each pixel so as to face the electrophoretic mixture; the process comprising:
placing an adsorbing member to which the electrophoretic particles have been temporarily adsorbed in a position opposite to one of the pair of substrates, and
transferring the electrophoretic particles onto the one substrate.
According to another aspect of the present invention, the above-mentioned display device is produced through a process comprising:
forming the partitioning walls on one of the pairs of substrates before the substrates are disposed with the prescribed gap therebetween to thereby define the plurality of pixels, and
distributing a distribution liquid containing the electrophoretic particles dispersed therein to the respective pixels in substantially equal amounts.